Correlation Between Shell Size and Presence and Size of Apertural Teeth in the Low-Intertidal Zone Snail, Nucella lamellosa

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Abstract

The low-intertidal zone marine gastropod, Nucella lamellosa, exhibits remarkable phenotypic plasticity between habitats as close as 100 m from one other. Shells that develop in different environments can display variation in color, banding, shape, sculpture, and thickness, and the most documented explanation for this variation is predator-induced resistance. The snails collected from the beach in front of the Friday Harbor Laboratories are of the thick-shelled variety of N. lamellosa and are known to exhibit a row of teeth within their apertural openings, presumably as a defense against their predator, Cancer productus. I collected 25 of these snails at low tide and took systematic measurements (length, width, weight) to quantify shell size, and I used high resolution images of the apertural openings to measure average tooth height and apertural lengths. I found that, while a majority of the snails (19 out of 25) displayed apertural teeth, there were 5 snails that did not (one snail exhibited drastically different morphology). Of the range of shell lengths I collected (1.03 cm – 5.84 cm), the largest snail without apertural teeth was 1.93 cm. By comparing shell width and weight to shell length, I determined that there was no significant difference between the way snails with and without apertural teeth developed; both groups showed a significant positive correlation between shell width and weight and shell length. I also found that for those snails with apertural teeth, there was a significant positive correlation between apertural length and apertural tooth height.